Simple Strategy for Producing Superhydrophobic Nanocomposite Coatings In Situ on a Building Substrate

Abstract

Numerous superhydrophobic materials have been developed in recent years by using a combination of two strategies: reducing the surface free energy and roughening the surface. Most of these procedures have the serious drawback of involving tedious multistage processes, which prevent their large-scale application, such as on the external stone and similar material surfaces of buildings exposed to the weather. This paper describes an innovative synthesis route for producing superhydrophobic surface coatings. The coating can even be produced, outdoors, on the building by a low-cost process. We demonstrate that the addition of silica nanoparticles to a mixture of organic and inorganic silica oligomers in the presence of a surfactant produces a coating of closely packed particles. The effect of this is to trap air beneath the water droplets, thus significantly minimizing the contact area between droplet and surface. The organic component reduces the surface free energy of the material, resulting in a high static contact angle. This has the effect of repelling water because the water droplets that form simply roll rapidly down the coated surface. The surfactant plays a valuable role, acting as a sol-gel transition catalyst and, by coarsening the pore structure of the gel network, prevents the coating material from cracking.

Nanocomposite Coatings: Preparation, Characterization, Properties, and Applications

“…By this sol-gel process, Facio and Mosquera [38] also successfully fabricated the nanocomposite coatings containing (i) a mixture of monomeric and oligomeric ethoxysilanes, (ii) a hydroxyl-terminated polydimethylsiloxane, (iii) colloidal silica particles, and (iv) a surfactant (n-octylamine). In addition, the sol-gel method could be used in combination with the electrodeposition for incorporation of inorganic nanofillers into the organic matrix [78] or into inorganic matrix [84].…”

“…For organic matrix, called polymer-based nanocomposite, the most used polymers for preparation of nanocomposite coating can be listed as follows: epoxy [2][3][4][5][6][7], polyurethane [8,9], Chitosan [10,11], polyethylene glycol (PEG) [12][13][14][15], polyvinylidene fluoride (PVDF) [16], PANi [17][18][19], PPy [20][21][22][23], polystyrene [24], polyamic acid and polyimide [25], rubber-modified polybenzoxazine (PBZ) [26], polymers containing reactive trimethoxysilyl (TMOS) [27], pullulan [28], fluoroacrylic polymer [29,30], ethylene tetrafluoroethylene (ETFE) [31], polyacrylate [3], poly(N-vinyl carbazole) [32], polycarbonate [33], fluorinated polysiloxane [34], polyester [35], polyacrylic [36], polyvinyl alcohol (PVA) [37], polydimethylsiloxane [38], polyamide [39], and UV-curable polymers [40].…”

New Consolidant-Hydrophobic Treatment by Combining SiO2 Composite and Fluorinated Alkoxysilane: Application on Decayed Biocalcareous Stone from an 18th Century Cathedral

“…By comparing CA values obtained in samples treated with UCA-T and UCA-TS, similar values are obtained, showing a slight increase for the gel containing silica nanoparticles. This can be related to the increase in roughness produced by particles in the surface of the stone [13,33]. Table S1 show water droplet static and dynamic contact angle (CA) values.…”

“…However, this change does not produce modifications in repellence behavior because the original topography of the stone surface is hardly modified by the coating (see Figure 4). Consequently, as the biocalcareous stone is a high porosity material composed of macropores with distance between roughness peaks in the micrometer range, and a significantly lower distance between roughness peaks in the nanometer range is required to produce a Cassie-Baxter regime [13,33,47]. The coating containing nanoparticles (UCA-TS) cannot produce a repellent surface on which the water droplets do not stick [48].…”

“…In the last years, we have prepared crack-free nanomaterials for stone conservation [7][8][9][10][11][12][13][14][15][16][17][18]. Specifically, the addition of an aqueous solution of n-octylamine to an alkoxysilane produces inverse micelles, which act as nanoreactors, generating silica seeds.…”